Damper having torque limiter function

ABSTRACT

A damper includes an outer cover having a front cover and a rear cover. The covers are joined to form a lubricant oil accommodation chamber for accommodating liquid. A damper device, a limiter mechanism, a first plate including a first collar portion located toward the front of the limiter mechanism, and a second plate including a second collar portion located toward the rear of the limiter mechanism are arranged in the outer cover. The limiter mechanism includes a first limiter plate, which is an input side on the torque transmission path, a second limiter plate, which is an output side on the torque transmission path, and a limiter disc spring, which presses the limiter plates.

TECHNICAL FIELD

The present invention relates to a wet-type damper capable of absorbingtorque vibration generated at a power source such as an engine andhaving a torque limiter function.

BACKGROUND ART

In a vehicle, a damper is usually arranged in a torque transmission pathto absorb torque vibration, which is generated at a power source such asan engine or an electric motor. When a large torque is generated at thepower source, such a damper blocks the transmission of torque from oneside of the torque transmission path to the other side of the torquetransmission path with a limiter mechanism (see Japanese Laid-OpenPatent Publication No. 2008-274968).

Japanese Laid-Open Patent Publication No. 2008-274968 describes a damper(hereinafter referred to as “conventional damper”), which is of awet-type damper used in a so-called hybrid vehicle, which uses an engineand an electric motor as a power source. As shown in FIG. 13, theconventional damper includes an outer case 303, which is formed by afront cover 301 serving as a first cover and a rear cover 302 serving asa second cover. The front cover 301, which is generally cylindrical andhas a closed bottom, is connected to an output shaft of the engine. Therear cover 302, which is generally annular when viewed from the front,is welded and fixed to the circumference of the front cover 301. Theouter case 303 is filled with lubricant oil serving as a liquid. Asleeve 304 projects rearward from a radially inner portion of the rearcover 302. A planetary gear mechanism (not shown) has an input shaft(output member) 305, the front end of which is inserted into the outercase 303.

The outer case 303 houses a generally cylindrical hub 306, a damperdevice 307, and a limiter mechanism 308. The hub 306 is supported to beintegrally rotatable with the input shaft 305 of the planetary gearmechanism. The damper device 307 is arranged radially outward from thehub 306. The limiter mechanism 308 is arranged radially outward from thedamper device 307. The damper device 307 includes an annular centralplate 309, to which the torque from the power source is transmittedthrough the limiter mechanism 308, and an annular intermediate member310, which is supported to be integrally rotatable with by the hub 306.A torque absorber 312 is arranged in the torque transmission pathbetween the central plate 309 and the intermediate member 310. Thetorque absorber 312 has a damper spring 311 serving as an elastic memberthat is elastic in the circumferential direction.

The limiter mechanism 308 includes an annular disc spring (limiterbiasing member) 313 and a limiter plate 314. The disc spring 313 issupported by a radially outer portion of the rear cover 302. The limiterplate 314 is arranged between the disc spring 313 and a radially outerportion of the central plate 309. The disc spring 313 applies biasingforce to the limiter plate 314, which further applies to biasing forceto the central plate 309. At the radially outer portion of the centralplate 309, friction members 315 and 316 are respectively arranged on thesurface of the central plate 309 facing toward the limiter plate 314,and a front surface of the central plate 309 facing toward the radiallyouter portion of the bottom of the front cover 301. The limiter plate314 pushes the central plate 309 via the friction member 315 with thebiasing force of the disc spring 313. The central plate 309 furtherpushes the bottom of the front cover 301 via the friction member 316.Thus, when the outer case 303 rotates, frictional force is generatedbetween the friction member 315 and the limiter plate 314 and betweenthe friction member 316 and the front cover 301. This rotates thecentral plate 309 with the outer case 303.

If the torque from the power source does not reach a predeterminedtorque, the torque from the power source is transmitted via the outercase 303, the limiter mechanism 308, the damper device 307, and the hub306 to the input shaft 305 of the planetary gear mechanism. If anexcessively large torque is generated and the torque exceeds apredetermined torque when the vehicle is driven by the engine or whenstarting the engine with the electric motor, slipping occurs between thelimiter mechanism 308 and the central plate 309 of the damper device307. In other words, if torque that is greater than the frictional forcegenerated between the limiter mechanism 308 and the damper device 307 isinput to the conventional damper, the transmission of an excessivelylarge torque between the limiter mechanism 308 and the damper device 307is blocked.

When assembling the outer case 303 in the conventional damper, the frontcover 301 is welded to the rear cover 302 in a state in which the damperdevice 307 and the limiter mechanism 308 are accommodated in the rearcover 302. In this state, the frontward biasing force of the disc spring313 in the limiter mechanism 308 is applied via the limiter plate 314and the central plate 309 to the front cover 301. Thus, the radiallyouter portion of the front cover 301 must be welded with the radiallyouter portion of the rear cover 302 while pressing the front cover 301against the rear cover 302 to maintain the predetermined positionalrelationship of the covers 301 and 302 in the axial direction. Sincepressing force must be applied to the front cover 301 or the rear cover302 when coupling the covers 301 and 302, the assembling of the outercase 303 is extremely difficult.

Furthermore, the front cover 301 may be deformed when pressed againstthe rear cover 302 when assembling the outer case 303.

Moreover, the friction members 315 and 316 have friction coefficients(μ) that generally vary greatly. Thus, the limiter mechanism 308 may notfunction even if the predetermined torque cannot be reached. Inparticular, with a dry-type friction member, the friction coefficient(μ) increases when its engagement surface becomes rusted. This mayoverly increase the torque (critical torque) at which torquetransmission is blocked. As a result, excessive torque may inflictdamages to the damper and other mechanisms in the torque transmissionpath.

Accordingly, in the prior art, each mechanism arranged in a torquetransmission path must be designed taking into consideration thevariations in critical torque. This inevitably enlarges each mechanism.For example, the outer diameter of the input shaft 305 in the planetarygear mechanism must be increased, and the dimensions of the damperspring 311 must be increased.

Additionally, an impact torque is alleviated and absorbed as the damperspring 311 compresses and deforms. Thus, the damper spring 311 has arelatively low spring constant so as to be suitable for alleviating suchimpact torque. In contrast, however, a large impact torque may not besufficiently alleviated if the spring constant is lowered. Further, theenergy of the impact torque cannot be readily absorbed just with thedamper spring 311.

It is an object of the present invention to provide a damper that allowsfor an outer case to be easily assembled without being deformed. It isanother object of the present invention to provide a damper thatsuppresses variations in the friction coefficient of a friction memberto stabilize the critical torque, while smoothly alleviating a largeimpact torque.

DISCLOSURE OF THE INVENTION

To achieve the above objects, one aspect of the present inventionprovides a damper arranged in a torque transmission path that transmitstorque from a power source to an output member rotated about apredetermined axis. The damper includes a housing, a damper device, alimiter mechanism, and a separation restriction member. The housing isrotated about the axis and includes a first cover and a second coverarranged along the axis. The first and second covers are joined to forma liquid accommodation chamber which accommodates a liquid. The damperdevice is arranged in the liquid accommodation chamber and capable ofabsorbing torque fluctuation transmitted through the housing. Thelimiter mechanism is arranged in the liquid accommodation chamber andincludes an input side portion located at an input side of the torquetransmission path, an output side portion arranged opposing the inputside portion and located at an output side of the torque transmissionpath, and a limiter biasing member which applies a biasing force to atleast one of the input side portion and the output side portion in adirection that the input side portion and the output side portionapproach each other. The separation restriction member is arranged inthe liquid accommodation chamber. The separation restriction memberrestricts relative movement of the first cover and the second covercaused by the biasing force from the limiter biasing member in adirection that separates the first cover and second cover from eachother.

In the above structure, the separation restriction member suppressesrelative movement of the covers such that they move away from each otherdue to the biasing force of the limiter biasing member in the limitermechanism. More specifically, when the two covers are joined in a statein which the damper device and the limiter mechanism are accommodated inthe liquid accommodation chamber, the separation restriction membersuppresses relative movement of the covers in a direction in which theyare separated from each other which is along an axial direction. Sincechanges in the positional relationship of the two covers in the axialdirection are suppressed, there is no need to apply force for pressingone of the two covers against the other one when joining the two covers.Therefore, in comparison with when joining the two covers while applyinga pressing force to one of the two covers, the probability of an outercase being deformed when joining the two covers is reduced. Further,since pressing force does not have to be applied to at least one of thetwo covers, the assembling of the damper is facilitated.

Preferably, the separation restriction member includes a firstrestriction portion arranged on one side of the limiter mechanism in theaxial direction and a second restriction portion arranged on the otherside of the limiter mechanism in the axial direction. Further, the firstand second restriction portions are arranged so as to maintain thedistance therebetween.

The above structure maintains the distance between the first restrictionmember and the second restriction member, which are arranged along theaxial direction, even if the biasing force of the limiter biasing memberin the limiter mechanism arranged between the first and secondrestriction members is applied to the first and second restrictionmembers. Accordingly, relative movement of the covers such that theymove away from each other due to the biasing force of the limiterbiasing member is suppressed. That is, pressing force does not have tobe applied to at least one of the two covers when joining the two coverssince changes in the positional relationship of the two covers in theaxial direction are suppressed.

Preferably, the separation restriction member is supported by adownstream side member, which is located downstream from the limitermechanism in the torque transmission path, so as to be integrallyrotatable with the downstream side member in a state in which movementof each of the first and second restriction portions in the axialdirection is suppressed.

In the above structure, the separation restriction member is supportedby the downstream side member in a state in which movement of eachrestriction portion in the axial direction is suppressed. Thissuppresses the application of biasing force to the two covers in adirection in which the covers are separated from each other.

Preferably, the limiter mechanism is arranged inward from the damperdevice in a radial direction of the damper that is orthogonal to theaxis.

With the above structure, in comparison to when the limiter mechanism isarranged outward from the damper device in the radial direction of thedamper, the damper may entirely be more miniaturized in the radialdirection.

Preferably, the damper further includes a coupling member coupled to theoutput member in the housing in a manner integrally rotatable with theoutput member. The coupling member supports the separation restrictionmember in an integrally rotatable state.

In the above structure, the separation restriction member is supportedby the coupling member. Thus, force for separating the two covers fromeach other, which is based on biasing force of the limiter biasingmember, is not applied to the two covers.

Preferably, the damper further includes a hysteresis mechanism arrangedin the liquid accommodation chamber. The hysteresis mechanism isconfigured to function when a rotation difference of the housing and theoutput member in a rotation direction about the axis becomes equal to apredetermined rotation difference. The hysteresis mechanism is arrangedinward from the damper device and the limiter mechanism in a radialdirection of the damper that is orthogonal to the axis.

With the above structure, in comparison to when the hysteresis mechanismis arranged outward from the damper device and the limiter mechanism inthe radial direction of the damper, the damper may entirely be moreminiaturized in the radial direction.

Preferably, the damper further includes a cylindrical coupling memberand an annular supporting member. The coupling member coupled to theoutput member in the housing in a manner integrally rotatable with theoutput member. The supporting member is arranged on a circumferentialside of the coupling member and supported by the coupling member in astate integrally rotatable with the coupling member. The coupling memberincludes a flange arranged at a position separated from the supportingmember in the axial direction along the axis and arranged to form aninstallation space between the flange and the supporting member in theaxial direction. The hysteresis mechanism includes a friction generationunit, which is arranged in the installation space, and a rotation unit,which is rotated with the housing by torque transmitted from the housingwhen a rotation difference between the housing and the output memberbecomes equal to a predetermined rotation difference. The frictiongeneration unit is configured to generate frictional force with therotation unit that suppresses rotation of the rotation unit when therotation unit rotates with the housing.

In the above structure, when the rotation difference of the housing andthe output member becomes equal to a predetermined rotation difference,frictional force suppressing rotation of the rotation unit and thehousing is generated between the friction generation unit and therotation unit. Thus, torque fluctuation transmitted to the housingbecomes such that the rotation difference of the housing and the outputmember exceeds the predetermined rotation difference, the hysteresismechanism decreases the torque fluctuation.

Preferably, the rotation unit includes a contacted portion arranged inthe installation space. The friction generation unit includes a contactmember, which is movable in the axial direction and contacts thecontacted portion of the rotation unit, and a hysteresis biasing member,which applies a biasing force to the contact member so that the contactmember presses the contacted portion.

The above structure prevents the biasing force of the hysteresis biasingmember of the friction generation unit from acting on the housing. Thatis, the biasing force from the hysteresis biasing member that biases thetwo covers away from each other along the axial direction is preventedfrom acting on at least one of the two covers. This suppressesdeformation of the outer case during assembling and facilitates theassembling of the outer case.

Preferably, the damper device includes a first torque transmission unit,a second torque transmission unit, and an elastic member. The firsttorque transmission unit is arranged in the housing in a torquetransmittable state. The second torque transmission unit is arranged atthe same position as the first torque transmission unit in the radialdirection of the damper and configured to be torque transmittable to theoutput member. The elastic member is elastic in a circumferentialdirection of which center is the axis and arranged in a torquetransmittable state between the first torque transmission unit and thesecond torque transmission unit in the circumferential direction.

In the above structure, the elasticity of the elastic member absorbstorque fluctuations transmitted from the power source.

Preferably, the first torque transmission unit is arranged in thehousing in a state integrally rotatable with the housing, and the inputside portion of the limiter mechanism is connected to the second torquetransmission unit in a torque transmittable state.

Generally, a damper device includes an annular drive side member, whichis discrete from the housing, and the drive side member is fixed to thehousing in an integrally rotatable state. Further, a first torquetransmission unit is formed by the drive side member. However, in thepresent invention, the drive side member is eliminated, and the firsttorque transmission unit is arranged in the housing. The elimination ofthe drive side member allows for miniaturization of the damper in theaxial direction.

Preferably, the covers are joined by welding a first fixing portion ofthe first cover to a second fixing portion of the second cover, whichfaces toward the first fixing portion.

In the above structure, the two covers may be joined by welding aradially outer portion of the second cover to a radially outer portionof the first cover even if a force for pressing the covers toward eachother is not applied to at least one of the two covers. This suppressesdeformation of the outer case and facilitates the assembling of theouter case.

A further aspect of the present invention provides a damper incorporatedin a power transmission mechanism for a hybrid vehicle. The damperincludes a housing and a damper device. The housing includes a firstcover and a second cover joined with each other. The housing is coupledto a drive plate and filled with lubricant oil. The damper device isarranged in the housing. The damper device includes a plurality ofdamper springs, a central disc, which is a torque input side portion, afirst friction member arranged in a peripheral portion of the centraldisc, a limiter plate arranged to face toward the first friction member,a first biasing member, a hub, a first plate and a second plate, whichare torque output side portions, a second friction member, and a secondbiasing member. The first biasing member pushes the limiter plate sothat the central disc is arranged between the limiter plate and thehousing. The hub has a shaft hole arranged at a center of the damperdevice and fitted to an output member. The first plate and second plateare arranged on opposite sides of the central disc. The second frictionmember is arranged between the torque output side portion and thecentral disc. The second biasing member biases the second frictionmember. The second friction member suppresses relative rotation of thecentral disc and the torque output side portion that is greater than orequal to a certain level with slip friction generated when the dampersprings are deformed.

Preferably, peripheral portions of the first plate and the second plateare spaced from the central disc so as not to contact the central disc,and inner portions of the first plate and second plate are contactablein a slipping manner with the central disc.

Preferably, the second friction member engages an engagement grooveformed in the central disc so as to be rotatable relative to the centraldisc in a predetermined rotation angle range, and the second frictionmember generates a slip friction when a relative rotation angle betweenthe central disc and the torque output side portion becomes greater thanor equal to a certain angle.

Preferably, the central disc is generally ring-shaped and includes aninner portion in which spring holders are arranged, in which two dampersprings are arranged in series between adjacent ones of the springholders. The hub includes a flange supporting an intermediate memberhaving an engagement groove. A separator projecting from an outercircumference of the intermediate member is arranged between the twodamper springs. The second friction member engages the engagement grooveof the intermediate member so as to be rotatable relative to theintermediate member in a predetermined rotation angle range. The secondfriction member generates slip friction when a relative rotation anglebetween the central disc and the torque output side portion becomesgreater than or equal to a certain angle.

Preferably, the hub includes a flange having first to third discportions that are concentric and have different outer diameters. Thesecond biasing member is attached to the first disc portion having thesmallest diameter. A washer and the second friction member are attachedto the second disc portion having an intermediate outer diameter. Thewasher and the second friction member are arranged between the firstplate and the third disc portion having the largest diameter in a statein which a biasing force of the second biasing member is applied. Anengagement piece is arranged in the washer engages with an engagementhole of the first plate.

Another aspect of the present invention provides a damper incorporatedin a power transmission mechanism for a hybrid vehicle. The damperincludes a housing and a damper device. The housing includes a firstcover and a second cover joined with each other. The housing is coupledto a drive plate and filled with lubricant oil. The damper device isarranged in the housing. The damper device includes a central disc, afirst friction member arranged at a peripheral portion of the centraldisc, a limiter plate arranged to face toward the first friction member,a first biasing member, a hub, a first plate and second plate, an outputside disc, which is a torque output side portion, a plurality of dampersprings, a second frictional member, and a second biasing member. Thefirst biasing member pushes the limiter plate so that the central discis arranged between the limiter plate and the housing. The hub has ashaft hole arranged at a center of the damper device and fitted to anoutput member. The first plate and second plate are arranged at oppositesides of the central disc and coupled to the central disc. The firstplate and second plate configure a torque input side portion with thecentral disc. The output side disc is fixed to the hub and arrangedbetween the first plate and the second plate. The plurality of dampersprings are accommodated in a spring accommodation hole formed betweenthe first plate and the second plate. The damper springs elasticallycouple the torque input side portion and the output side disc. Thesecond friction member is arranged between the output side disc and thetorque input side portion. The second biasing member biases the secondfriction member. The second friction member suppresses relative rotationof the torque input side portion and the output side disc that isgreater than or equal to a certain level with slip friction generatedwhen the damper springs deform.

Preferably, the first plate and the second plate are contactable in aslipping manner with an inner portion of the output side disc.

Preferably, the second friction member engages an engagement grooveformed in at least one of the first plate and the second plate so as tobe rotatable in a predetermined rotation angle range relative to atleast one of the first plate and the second plate. The second frictionmember generates a slip friction when a relative rotation angle betweenthe torque input side portion and the output side disc becomes greaterthan or equal to a certain angle.

Preferably, the output side disc is generally ring-shaped and includes aperipheral portion in which spring holders are arranged, in which twodamper springs are arranged in series between adjacent ones of thespring holders. The ring-shaped central disc includes an inner portionsupporting an intermediate member having an engagement groove. Aseparator projecting from an inner circumference of the intermediatemember is arranged between the two damper springs. The second frictionmember engages the engagement groove of the intermediate member so as tobe rotatable relative to the intermediate member in a predeterminedrotation angle range. The second friction member generates slip frictionwhen a relative rotation angle between the torque input side portion andthe output side disc becomes greater than or equal to a certain angle.

Preferably, the hub includes a flange having first to third discportions that are concentric and have different outer diameters. Thesecond biasing member is attached to the first disc portion having thesmallest diameter. A washer and the second friction member are attachedto the second disc portion having an intermediate outer diameter. Thewasher and the second friction member are arranged between the outputside disc and the third disc portion having the largest diameter in astate in which a biasing force of the second biasing member is applied.An engagement piece arranged in the washer engages with an engagementhole of the output side disc.

With the damper according to the present invention, the damper andlimiter are arranged between a crankshaft and an input shaft whentransmitting the torque of the crankshaft to the input shaft. This basicstructure is the same as the prior art. The damper device arranges thecentral disc between the first plate and the second plate and includesthe plurality of damper springs. Relative rotation of the central discand the two plates compresses and deforms the damper springs. The firstfriction member is arranged on the outer circumference of the centraldisc. The biasing force of the first biasing member is applied to thelimiter plate, which attaches the first friction member to the outercircumference, so as to generate frictional force with the firstfriction member. A disc spring is normally used as the first biasingmember. However, the first biasing member is not particularly limited insuch a manner.

The damper of the present invention is a wet type structure and therebyincludes a housing, which houses the damper device. The housing isfilled with lubricant oil. The housing is formed by welding the firstcover and the second cover, which also function as a flywheel. The hubis attached to the center of the damper, and the input shaft is fittedto a shaft hole of the hub.

The central disc of the damper is arranged between the first plate andthe second plate. However, an inner circumferential portion of the twoplates is contactable in a slipping manner with the central disc, and aslight gap is provided at other regions so as not to contact the centraldisc. Further, the second friction member is attached in a sandwichedstate so that biasing force is applied to the peripheral portion of thehub so as to suppress rotation. The second frictional member engageswith the central disc, and frictional resistance is applied to therotation of the central disc.

The second frictional member, which is engaged with the central disc,has a predetermined margin. However, the second friction member isforced so as to function when relative rotation of the first plate andsecond plate becomes greater than or equal to a certain angle. Thesecond friction member is engaged with an intermediate member, whichuses two damper springs arranged in series. The second friction membermay be attached to engage the first plate and second plate, which serveas the torque output side portion. In addition, the attachment positionis not limited to the outside of the hub.

The present invention may have a structure in which the first plate andsecond plate, which are arranged on opposite sides of the central disc,serve as a torque input side portion, and a discrete output side disc isarranged on the inner circumference of the torque input side portion. Inthis case, the second friction member may be arranged between the outputside disc and the plate of the torque input side portion, and whenbiasing force is applied to the second friction member and deformationof the damper springs generate torsion rotation of the central disc ofthe torque input side portion and the output side disc that is greaterthan or equal to a certain level, the relative torsion rotation may besuppressed with slip friction.

The damper according to the present invention may be of a wet typestructure in which the damper is accommodated in a housing, and thehousing is filled with lubricant oil. Accordingly, the first frictionmember of the limiter always has a constant friction coefficient. Inother words, the engagement surface of the first friction member doesnot rust, variation of the critical torque is suppressed, and thecritical torque may be decreased. This allows for the setting of arelatively low critical torque. Thus, the diameter of a shaft forming apower transmission mechanism and a gear mechanism may be decreased, andthe entire damper may be reduced in size.

The damper device in the damper according to the present inventionincludes a plurality of damper springs. The damper springs arecompressed and deformed when impact torque acts on the central discserving as a torque input side portion so as to alleviate the impacttorque to absorb engine torque fluctuation. In such a case, when thecompression of the damper springs rotates the first plate and secondplate serving as a torque output side portion, the central disc is incontact with the two plates and the inner portion. Thus, a large slipfriction torque is not generated. Further, the damper springs areelastically deformed in the lubricant oil. Thus, a large frictionalresistance is not generated even when contacting the inner surface of anaccommodation area of the plate.

Further, when the damper springs are compressed and deformed by acertain degree, the second friction member is rotated, and the secondfriction member to which biasing force is applied contacts the centraldisc or the two plates and generates a large frictional resistance.Accordingly, the damper alleviates the impact torque and absorbs energyproduced by the impact torque. This readily attenuates and stops theelastic motion of the damper springs.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic block diagram showing a hybrid system according toa first embodiment of the present invention;

FIG. 2 is a cross-sectional view showing a damper of FIG. 1;

FIG. 3 is a plan view showing a front cover of FIG. 2 from the rear;

FIG. 4 is a plan view showing the interior of a damper from the frontcover;

FIG. 5 is a schematic plan view showing part of a rotation unit in ahysteresis mechanism of FIG. 2;

FIG. 6 is a schematic cross-sectional view showing another example of alimiter mechanism according to the first embodiment of the presentinvention;

FIG. 7 is a cross-sectional view showing a damper according to a secondembodiment of the present invention;

FIG. 8 is a partially cross-sectional plan view showing the damperdevice of FIG. 7;

FIG. 9 is a partially enlarged view showing a center shaft part of thedamper device;

FIG. 10 is a cross-sectional view showing a power transmission mechanismsecured to the damper of FIG. 7;

FIG. 11 is a schematic diagram showing specific examples of a damper;

FIG. 12 is a cross-sectional view showing a damper according to a thirdembodiment of the present invention; and

FIG. 13 is a cross-sectional view showing a conventional damper.

BEST MODE FOR CARRYING OUT THE INVENTION

A first embodiment of a damper, which is installed in a hybrid vehicle,according to the present invention will now be discussed with referenceto FIGS. 1 to 5. In the description of the present specificationhereinafter, the “front side” refers to the right side as viewed in FIG.2, and the “rear side” refers to the left side as viewed in FIG. 2.

As shown in FIG. 1, a hybrid drive device 11 mounted on the hybridvehicle includes an engine 12, which is a first power source, anelectric motor 13, which is a second power source driven by powersupplied from a battery (not shown), and a damper 14, which absorbsfluctuation in the torque generated by the engine 12 and the electricmotor 13 (hereinafter referred to as “torque fluctuation”). The hybriddrive device 11 also includes a planetary gear mechanism 15, to whichthe torque from the engine 12 transmitted via the damper 14 and thetorque from the electric motor 13 are transmitted.

The planetary gear mechanism 15 includes a sun gear, a pinion gear, aplanet carrier, and a ring gear (not shown). Torque transmitted by thedamper 14 from the engine 12 is transmitted to the planet carrier via aninput shaft 16, which serves as an output member. In a state in whichtorque is transmittable, the electric motor 13 and a sprocket 17 arecoupled to the ring gear (not shown) of the planetary gear mechanism 15.When the ring gear is rotated by the torque from at least either one ofthe engine 12 and the electric motor 13, the torque is transmitted to areduction gear mechanism (not shown) via the sprocket 17 and a chain 18running around the sprocket 17. Furthermore, a power generation motor 19is coupled to the sun gear (not shown) of the planetary gear mechanism15. The power generation motor 19 generates power when torque istransmitted via the sun gear. The generated power is supplied to thebattery via an inverter (not shown). In other words, the battery ischarged when the power generation motor 19 is driven.

When the engine 12 is driven, the torque from the engine 12 istransmitted to the planetary gear mechanism 15 through the damper 14,and the planet carrier of the planetary gear mechanism 15 rotates. Therotation of the planet carrier rotates the ring gear and transmits thetorque from the engine 12 to the sprocket 17. When the sprocket 17rotates, the torque from the engine 12 is transmitted to drive wheels bythe chain 18, the reduction gear mechanism, and the like thereby movingthe vehicle. In this state, the sun gear is also rotated by the rotationof the planet carrier in the planetary gear mechanism 15. This drivesthe power generation motor 19 and charges the battery.

When the engine 12 stops running and the electric motor 13 is driven,torque is transmitted from the electric motor 13 to the ring gear of theplanetary gear mechanism 15, and the rotation of the ring gear rotatesthe sprocket 17. When the sprocket 17 rotates, the torque from theelectric motor 13 is transmitted to the drive wheels by the chain 18,the gear reduction mechanism, and the like thereby moving the vehicle.In this state, the torque from the electric motor 13 is not transmittedto the engine 12. In the hybrid drive device 11, the engine 12 and theelectric motor 13 may both be driven to move the vehicle.

The damper 14 of the present embodiment will now be discussed withreference to FIGS. 1 to 5.

Referring to FIGS. 1 and 2, the damper 14 of the present embodiment isarranged in a torque transmission path, which transmits the torque fromthe engine 12 to the input shaft 16 of the planetary gear mechanism 15.The input shaft 16 is rotatable about a predetermined axis S (shown by asingle-dash line in FIG. 2), which extends toward the front and rear ofthe vehicle. Specifically, the damper 14 includes an outer case 23serving as a housing. The outer case 23 includes a front cover (firstcover) 21, which is generally cylindrical and has a closed bottom, and arear cover (second cover) 22, which is generally annular when viewedfrom the front. A lubricant oil accommodation chamber 24, which servesas a liquid accommodation chamber, is formed between the covers 21 and22 in the outer case 23. The lubricant oil accommodation chamber 24 isfilled with lubricant oil serving as a liquid. In the lubricant oilaccommodation chamber 24, a damper device 25, a limiter mechanism 26,and a hysteresis mechanism 27 are arranged in this order from the outerside towards the inner side with respect to the radial direction of thedamper 14, which is orthogonal to the axis S.

The front cover 21 includes a bottom portion 21 a, which is generallydisc-shaped when viewed from the front and which center conforms to theaxis S, and a cylindrical portion 21 b, which is formed integrally withthe bottom portion 21 a. The cylindrical portion 21 b has a rear end(first fixing portion) 21 c welded to the rear cover 22.

The rear cover 22 includes a main cover body 22 a, and mount 22 b, and asleeve 22 c. The main cover body 22 a is generally annular when viewedfrom the front. The mount 22 b has a flange-shape and is locatedradially outward from the main cover body 22 a. The sleeve 22 c projectstoward the rear from a radially inner portion of the main cover body 22a. The main cover body 22 a, the mount 22 b, and the sleeve 22 c areformed integrally. The main cover body 22 a includes an outer portion(second fixing portion) 22 d, which is welded to the rear end 21 c ofthe cylindrical portion 21 b of the front cover 21. The mount 22 b ofthe rear cover 22 is coupled to a crankshaft 12 a (see FIG. 1), which isan output shaft of the engine 12, by a drive plate (not shown). Theouter case 23, to which torque is transmitted from the engine 12,rotates in a predetermined rotation direction R (see FIG. 2) about theaxis S.

The input shaft 16 of the planetary gear mechanism 15 has an axiallymiddle portion located in the sleeve 22 c of the rear cover 22. Further,the input shaft 16 has a front end located in the lubricant oilaccommodation chamber 24. The front end of the input shaft 16 has acircumferential portion that supports a hub 28, which serves as acoupling member, so that the hub 28 is integrally rotatable with theinput shaft 16. Specifically, the hub 28 is spline-fitted to the inputshaft 16. The hub 28 includes a hub tube 29, the center of whichconforms to the axis S, and a hub flange 30, which is located at thecircumferential side of the hub tube 29 and at the axially middle partof the hub tube 29. The hub tube 29 and the hub flange 30 are formedintegrally.

The hub flange 30 includes a first disc portion 30 a, which is locatedat the most radially inward side, a second disc portion 30 b, which islocated at the radially outward side of the first disc portion 30 a, anda third disc portion 30 c, which is located at the radially outward sideof the second disc portion 30 b. The axial length of the first discportion 30 a is the longest among the first to third disc portions 30 ato 30 c, and the axial length of the second disc portion 30 b is longerthan that of the third disc portion 30 c. In other words, the hub flange30 is formed such that the axial length becomes shorter towards theradially outward side.

Two plates 32 and 33 arranged next to each other in the axial directionare fixed to the first disc portion 30 a by a plurality of (only twoshown in FIG. 2) rivets 31. The rivets 31 are arranged along acircumferential direction of the hub 28 about the axis S. Thus, the twoplates 32 and 33 are rotated integrally with the hub 28. The first plate32, which serves as a supporting member, is arranged in front of thesecond plate 33. Further, the first plate 32 includes an annular firstbase portion 32 a, which is supported by the hub 28 and which centerconforms to the axis S, a first cylindrical portion 32 b, which extendstowards the front from a circumferential end of the first base portion32 a, and a first collar portion 32 c, which is disc-shaped and extendsradially from the front end of the first cylindrical portion 32 b. Thefirst base portion 32 a, the first cylindrical portion 32 b, and thefirst collar portion 32 c are formed integrally. The first cylindricalportion 32 b is formed so that its center conforms to the axis S and isarranged radially outward from the hub flange 30. The first collarportion 32 c is arranged such that a slight gap is formed between itsfront surface and the bottom portion 21 a of the front cover 21.Lubricant oil is held in the gap. Further, an annular hysteresisaccommodation chamber 34, which serves as an installation space, isformed between the hub flange 30 and the first base portion 32 a in theaxial direction. The hysteresis accommodation chamber 34 has an axiallength that becomes longer radially outward.

The second plate 33, which is located at the rear side of the firstplate 32, extends about the axis S and is generally annular when viewedfrom the front. The radially inner side of the second plate 33 defines asecond base portion 33 a, which contacts the first base portion 32 a ofthe first plate 32. The second plate 33 includes an intermediate portion33 b located radially outward and rearward from the second base portion33 a. A slight gap is formed between the intermediate portion 33 b andthe main cover body 22 a of the rear cover 22. The radially outwardportion of the intermediate portion 33 b in the second plate 33 definesan annular second collar portion 33 c, which is located at substantiallythe same axial position as the second base portion 33 a. A plurality of(only two shown in FIG. 2) through-holes 33 d are arranged at equalintervals along the circumferential direction about the axis S betweenthe intermediate portion 33 b and the second collar portion 33 c in theradial direction in the second plate 33. An annular limiteraccommodation chamber 35 is formed between the collar portions 32 c and33 c in the axial direction.

The damper device 25 is arranged in a damper accommodation chamber 36,which is formed radially outward from the limiter accommodation chamber35 in the lubricant oil accommodation chamber 24. As shown in FIGS. 2and 3, the damper device 25 includes a plurality of (six in the presentembodiment) first torque transmission units 37A and a plurality of (sixin the present embodiment) first torque transmission units 37B. Thefirst torque transmission units 37A are arranged on the radially outerpart of the bottom portion 21 a of the front cover 21. The first torquetransmission units 37B are arranged on the radially outer part of themain cover body 22 a of the rear cover 22. The first torque transmissionunits 37A are arranged on the front cover 21 at equal intervals in thecircumferential direction. The first torque transmission units 37B arearranged on the rear cover 22 are arranged in correspondence with thefirst torque transmission units 37A in the circumferential and radialdirections. A gap 38 is formed between each set of corresponding firsttorque transmission units 37A and 37B aligned in the axial direction soas to accommodate a main disc body 39 a of a damper disc 39, which willbe described later.

As shown in FIGS. 2 and 4, the damper device 25 includes the damper disc39, which is generally annular when viewed from the front and has acenter that conforms to the axis S. The damper disc 39 includes the maindisc body 39 a having an annular shape. The main disc body 39 a isarranged in the gap 38 free from contact with the first torquetransmission units 37A and 37B. In the main disc body 39 a, a pluralityof (six in the present embodiment) spring accommodation holes 40 arearranged at equal interval in the circumferential direction and areformed at substantially the same radial position as the first torquetransmission units 37A and 37B. Each spring accommodation hole 40 islocated between adjacent ones of the first torque transmission units 37Aand 37B in the circumferential direction. This forms second torquetransmission units 41 at circumferential positions substantiallycorresponding to the first torque transmission units 37A and 37B in themain disc body 39 a. Each spring accommodation hole 40 accommodates adamper spring 42 serving as an elastic member that is elastic in thecircumferential direction.

The damper disc 39 includes a plurality of (three in the presentembodiment) extensions 39 b extending rearward from a radially innerportion of the main disc body 39 a. The extensions 39 b are each formedto have a generally arcuate shape when seen from the front and arearranged at equal intervals in the circumferential direction. In otherwords, the extensions 39 b is arranged to surround the limiteraccommodation chamber 35. At the radially inner portion of the damperdisc 39, a support 43, which is supported to be integrally rotatablewith the damper disc 39, supports a plurality of first limiter plates50, which will be described later, of the limiter mechanism 26.

When the outer case 23 rotates in the predetermined rotation directionR, the damper springs 42 are pushed by the first torque transmissionunits 37A and 37B that are located at the upstream side with respect tothe rotation direction R. In other words, torque is transmitted from thefirst torque transmission units 37A and 37B to the damper spring 42. Thedamper springs 42 then push the second torque transmission units 41 ofthe damper disc 39 located at the downstream side with respect to therotation direction R and transmit torque from the first torquetransmission units 37A and 37B toward the damper disc 39. This rotatesthe damper disc 39 in the predetermined rotation direction R. In otherwords, the torque from the engine 12 is transmitted to the limitermechanism 26 via the outer case 23 and the damper device 25.

As shown in FIGS. 2 and 3, the damper device 25 includes a plurality of(three in the present embodiment) projections 44A and a plurality of(three in the present embodiment) projections 44B. The projections 44Aare formed radially inward from the first torque transmission units 37Aon the bottom portion 21 a of the front cover 21. The projections 44Bare formed radially inward from the first torque transmission unit 37Bon the main cover body 22 a of the rear cover 22. The projections 44Bare arranged at the same radial positions as the correspondingprojections 44A. The projections 44A and 44B are respectively arrangedbetween adjacent ones of the extensions 39 b in the circumferentialdirection. In other words, referring to FIGS. 3 and 4, the projections44A and 44B are each rotatable relative to the damper disc 39 in a space45 between adjacent ones of the extensions 39 b in the circumferentialdirection.

As shown in FIG. 2, the limiter mechanism 26 is arranged in the limiteraccommodation chamber 35. The limiter mechanism 26 includes a pluralityof (five in FIG. 2) first limiter plates (input side portion) 50. Thefirst limiter plates 50 are supported by the support 43, which islocated radially inward from the damper disc 39, so as to be movable inthe axial direction and integrally rotatable with the support.Specifically, as shown in FIG. 2, the first limiter plates 50 aresupported by the support 43 of the damper disc 39 by an elastic ringmember 50A. Each first limiter plate 50 has an annular shape. A firstfriction member 52 is arranged on both axial sides of the first limiterplate 50.

The limiter mechanism 26 also includes a plurality of (five in FIG. 2)second limiter plates (output side portion) 51. The second limiterplates 51 are supported by the cylindrical portion 32 b of the firstplate 32 so as to be movable in the axial direction and integrallyrotatable with the cylindrical portion 32 b. Each second limiter plate51 has an annular shape and is arranged between adjacent ones of thefirst limiter plates 50 in the axial direction and in front of the mostfrontward first limiter plate 50. In other words, each second limiterplate 51 is arranged to face toward the first limiter plate 50 that areadjacent in the axial direction.

The limiter mechanism 26 further includes a limiter disc spring 53serving as a limiter biasing member supported by the first collarportion 32 c of the first plate 32. The limiter disc spring 53 applies abiasing force rearwards to the limiter plates 50 and 51 so that thefirst friction members 52 push each first limiter plate 50 against thesecond limiter plates 51 located in front and rear of the first limiterplate 50. In other words, each first limiter plate 50 is sandwiched bythe second limiter plates 51 that are located at the front and rearsides of the first limiter plate 50. In this state, the biasing forceapplied toward the front from the limiter disc spring 53 is absorbed bythe first collar portion 32 c of the first plate 32. Thus, the biasingforce of the limiter disc spring 53 is not applied to the front cover21. The second plate 33 is configured to absorb the biasing forceapplied towards the rear side from the limiter disc spring 53 to thesecond collar portion 33 c by the limiter plates 50 and 51. Thus, thebiasing force from the limiter disc spring 53 is not applied to the rearcover 22.

Accordingly, in the present embodiment, the first plate 32 and thesecond plate 33 form a separation restriction member for restrictingrelative movement of the front cover 21 and the rear cover 22 in adirection in which they are separated from each other (axial direction)by the biasing force of the limiter disc spring 53. The hub 28supporting the first plate 32 and the second plate 33 also functions asa downstream side member located at the downstream side of the limitermechanism 26 in the torque transmission path. The first collar portion32 c of the first plate 32 functions as a first restriction portionarranged at one axial side (front side) of the limiter mechanism 26, andthe second collar portion 33 c of the second plate 33 functions as asecond restriction portion arranged at the other axial side (rear side)of the limiter mechanism 26.

As shown in FIG. 2, the hysteresis mechanism 27 is arranged in thedamper 14 radially inward from the limiter mechanism 26. Such hysteresismechanism 27 includes a friction generation unit 55 arranged in thehysteresis accommodation chamber 34. The friction generation unit 55includes an annular second friction member (contact member) 56 and ahysteresis disc spring 57, which serves as a hysteresis biasing member.The second friction member 56 is supported by the first cylindricalportion 32 b of the first plate 32 so as to be movable in the axialdirection and integrally rotatable with the first cylindrical portion 32b. The hysteresis disc spring 57 is arranged on the rear side of thesecond friction member 56. The hysteresis disc spring 57 is supported bythe first base portion 32 a of the first plate 32 and applies afrontward biasing force to the second friction member 56.

The hysteresis mechanism 27 also includes a rotation unit 58 forobtaining a state in which the torque from the case 23 is directlytransmittable to the hub 28 when a rotation difference 8 (also referredto as “torsion angle”) of the outer case 23 and the hub 28 becomes equalto a predetermined rotation difference θth (see FIG. 5). As shown inFIGS. 2 and 3, the rotation unit 58 includes an annular hysteresis plate59, which is supported to be integrally rotatable with the bottomportion 21 a of the front cover 21. A plurality of (twelve in thepresent embodiment) engagement recesses 60 formed at equal intervals inthe circumferential direction about the axis S as the center is formedin the outer circumference of the hysteresis plate 59.

The rotation unit 58 includes a hysteresis washer 61 arranged on thefront side of the second friction member 56 in the hysteresisaccommodation chamber 34. The hysteresis washer 61 is arranged to berotatable relative to the hub 28. The hysteresis washer 61 includes awasher body 61 a, which serves as an annular contacted portion. Aplurality of engagement pieces 61 b corresponding to the engagementrecesses 60 project frontward from the outer circumference edge of thewasher body 61 a. As shown in FIGS. 4 and 5, the engagement pieces 61 bare arranged at equal intervals along the circumferential direction ofthe hysteresis plate 59. Each engagement piece 61 b has a distal end(front end) arranged in the corresponding engagement recess 60. When therotation difference θ of the outer case 23 and the hub 28 becomes equalto a predetermined rotation difference θth, each engagement piece 61 bengages a circumferential end of the engagement recess 60 so that thehysteresis washer 61 rotates with the outer case 23. In this case, africtional force that reduces the force for rotating the hysteresiswasher 61 and the outer case 23 (also referred to as “rotation force”)and decreases the rotation difference θ of the outer case 23 and the hub28 is generates between the washer body 61 a of the hysteresis washer 61and the second friction member 56, which presses the washer body 61 a.

In FIG. 5, the width in the circumferential direction of the engagementrecess 60 and the size of the engagement piece 61 b arranged in theengagement recess 60 are shown in an exaggerated manner to facilitateunderstanding of the description.

The operation of the damper 14 of the present embodiment will now bediscussed.

When torque is transmitted from the engine 12 to the outer case 23, theouter case 23 rotates in the predetermined rotation direction R. Thisalso rotates the damper device 25 so that the torque from the engine 12is transmitted to the limiter mechanism 26 by the outer case 23 and thedamper device 25. In this case, frictional force is generated betweenthe adjacent limiter plates 50 and 51 in the axial direction. Thus, thesecond limiter plate 51 rotates in the predetermined rotation directionR with the first limiter plate 50. The rotation of the second limiterplates 51 then rotate the hub 28 and the input shaft 16 of the planetarygear mechanism 15. In other words, the torque from the engine 12 istransmitted to the planetary gear mechanism 15.

When torque that is greater than the frictional force, which isgenerated between the adjacent limiter plates 50 and 51 arranged onopposite sides of the first friction member 52, is transmitted to thefirst limiter plate 50 of the limiter mechanism 26 via the damper device25, the limiter plates 50 and 51 slip against one another. In otherwords, the torque transmission to the input shaft 16 of the planetarygear mechanism 15 is blocked by the limiter mechanism 26.

The hysteresis mechanism 27 functions when the torque fluctuation thatcannot be absorbed by the damper spring 42 of the damper device 25 istransmitted to the damper 14 and the rotation difference θ of the outercase 23 and the hub 28 becomes equal to the predetermined rotationdifference θth. Specifically, each engagement piece 61 b of thehysteresis washer 61 engages the circumferential end of thecorresponding engagement recess 60 in the hysteresis plate 59. In thiscase, a frictional force that reduces the rotation force of the outercase 23 is generated by the biasing force from the hysteresis discspring 57 between the washer body 61 a of the hysteresis washer 61 andthe second friction member 56. As a result, the hysteresis washer 61rotated when the outer case 23 rotates slides along the second frictionmember 56. The sliding speed of the hysteresis washer 61 is lowered bythe frictional force generated between the washer body 61 a and thesecond friction member 56. In other words, the torque fluctuationtransmitted to the damper 14 is absorbed by the hysteresis mechanism 27.

Further, the hysteresis mechanism 27 does not function when the rotationdifference θ of the outer case 23 and the hub 28 is less than thepredetermined rotation difference θth. In this state, the rotation ofthe outer case 23 is not restricted by the hysteresis mechanism 27.Thus, torque is transmitted from the engine 12 to the planetary gearmechanism 15 via the damper 14 with high efficiency.

Accordingly, the present embodiment has the advantages described below.

(1) The plates 32 and 33 arranged on opposite sides of the limiter discspring 53 in the axial direction of the limiter mechanism 26 suppressrelative movement of the covers 21 and 22 in directions in which theyare moved away from each other by the biasing force of the limiter discspring 53 of the limiter mechanism 26. In other words, when joining thecovers 21 and 22 in a state in which the damper device 25 and thelimiter mechanism 26 are accommodated in the lubricant oil accommodationchamber 24, relative movement of the covers 21 and 22 in directions inwhich they are moved away from each other in the axial direction issuppressed. Thus, the front cover 21 does not need to be pressed againstthe rear cover 22. This facilitates alignment of the front cover 21 withthe rear cover 22 in the axial direction. Since pressing force does nothave to be applied to at least one of the covers 21 and 22, the weldingof the covers 21 and 22 may be easily performed. In comparison with theprior art in which the front cover 21 must be pressed against the rearcover 22, deformation of the front cover 21 and the rear cover 22 issuppressed during assembling.

(2) The axial dimension of the limiter accommodation chamber 35accommodating the limiter mechanism 26 does not change even if thebiasing force of the limiter disc spring 53 is applied to at least oneof the plates 32 and 33 supported by the hub 28. The biasing force fromthe limiter disc spring 53 is thus not applied to the covers 21 and 22.Therefore, the front cover 21 may be maintained at a predeterminedposition relative to the rear cover 22 without pressing the front cover21 against the rear cover 22 during assembling.

(3) The plates 32 and 33 forming the separation restriction member aresupported by the hub 28 in a state immovable in the axial direction. Thehub 28 thus does not move in the axial direction even if the biasingforce from the limiter disc spring 53 is applied to the plates 32 and33. This restricts the force that moves away the covers 21 and 22 fromeach other generated from the biasing force of the limiter disc spring53.

(4) The limiter mechanism 26 is arranged in the damper 14 radiallyinward from the damper device 25. This contributes to furtherminiaturization of the damper 14 in the radial direction compared towhen the limiter mechanism 26 is arranged radially outward from thedamper device 25 in the damper 14.

(5) The hysteresis mechanism 27 is arranged in the damper 14 radiallyinward from the damper device 25 and the limiter mechanism 26. Thiscontributes to further miniaturization of the damper 14 in the radialdirection compared to when the hysteresis mechanism 27 is arrangedradially outward from the damper device 25 and the limiter mechanism 26in the damper 14.

(6) When the rotation difference θ of the outer case 23 and the hub 28becomes equal to the predetermined rotation difference θth, a frictionalforce that suppresses the rotation of the outer case 23 is generatesbetween the friction generation unit 55 and the washer body 61 a. Thus,even if fluctuation in the torque transmitted to the outer case 23 issuch that the rotation difference θ of the outer case 23 and the hub 28becomes equal to the predetermined rotation difference θth, such torquefluctuation is absorbed by the hysteresis mechanism 27.

(7) The friction generation unit 55 of the hysteresis mechanism 27 isarranged in the hysteresis accommodation chamber 34 between the hubflange 30 of the hub 28 and the first plate 32. Thus, the biasing forcefrom the hysteresis disc spring 57 of the friction generation unit 55does not act on the outer case 23. That is, the biasing force from thehysteresis disc spring 57 does not cause force to act on at least one ofthe covers 21 and 22 in a direction moving away the covers 21 and 22from each other. In other words, when joining the covers 21 and 22 in astate in which the damper device 25, the limiter mechanism 26, and thehysteresis mechanism 27 are accommodated in the lubricant oilaccommodation chamber 24, relative movement of the covers 21 and 22 inthe axial direction in which the covers 21 and 22 move away from eachother is suppressed. Thus, the front cover does not have to be pressedagainst the rear cover 22. This facilitates alignment of the front cover21 in the axial direction with respect to the rear cover 22. Further,since pressing force does not have to be applied to at least one of thecovers 21 and 22, the welding of the covers 21 and 22 is facilitated.Compared to the prior art in which the front cover 21 must be pressedagainst the rear cover 22, deformation of the front cover 21 and therear cover 22 during assembling is suppressed.

(8) Generally, a damper device includes a drive member, which isdiscrete from the two covers forming the outer case, and the drivemember includes a first torque transmission unit. The damper device 25of the present embodiment does not include the drive member, and thefirst torque transmission units 37A and 37B are directly arranged on theouter case 23. Thus, compared to the damper of the prior art thatincludes the damper device, the damper 14 may be miniaturized in theaxial direction since less components are arranged along the axialdirection.

The first embodiment may be modified as described below.

The damper device 25 may include an annular drive member supported to beintegrally rotatable with a member (outer case 23 in the firstembodiment) arranged on the upstream side of the damper device 25 in thetorque transmission path. In this case, the first torque transmissionunits are arranged on the drive member instead of the front cover 21 andthe rear cover 22. In such a structure, the damper 14 may be easilyassembled since the biasing force from the disc springs 53 and 57 is notapplied to the covers 21 and 22 although the entire length in the axialdirection of the damper 14 becomes longer than the above-describedembodiment.

The first torque transmission unit 37A may extend radially inward fromthe cylindrical portion 21 b of the front cover 21.

The first torque transmission unit 37A may be integrally formed with thefront cover 21. In the same manner, the first torque transmission unit37B may be integrally formed with the rear cover 22.

Either the first torque transmission unit 37A or the first torquetransmission unit 37B may be eliminated.

The hysteresis mechanism 27 may have a configuration in which a regioncorresponding to the washer body 61 a of the hysteresis washer 61, aregion corresponding to the second friction member 56, and a regioncorresponding to the hysteresis biasing member 57 are arranged along theradial direction of the damper 14. In such a structure, the biasingforce from the hysteresis biasing member does not act on the covers 21and 22.

The hysteresis mechanism 27 may be eliminated from the damper 14.Alternatively, in the damper 14, the hysteresis mechanism 27 may bearranged radially outward from the limiter mechanism 26 or radiallyoutward from the damper device 25.

The limiter mechanism 26 may be arranged radially outward from thedamper device 25. For example, as shown in FIG. 6, if a snap ring 75 isarranged in the rear side of the cylindrical portion 21 b of the frontcover 21, a limiter mechanism 26A may be arranged between the bottomportion 21 a of the front cover 21 and the snap ring 75 in the axialdirection. The limiter mechanism 26A includes the limiter disc spring53, the first limiter plate 50, and the second limiter plate 51. Thelimiter disc spring 53 is supported by the snap ring 75. The firstlimiter plate 50 is supported by the cylindrical portion 21 b of thefront cover 21 to be movable in the axial direction. The second limiterplate 51 is supported by the damper device 25, which is arrangedradially inward from the limiter mechanism 26A. A third friction member70 and a fourth friction member 71 are respectively arranged on oppositesides of the second limiter plate 51 in the axial direction. The thirdfriction member 70 slides along the first limiter plate 50, and thefourth friction member 71 slides along the bottom portion 21 a of thefront cover 21. The snap ring 75 prevents the first limiter plate 50from being separated from the front cover 21. The limiter disc spring 53is supported by the snap ring 75, and the limiter disc spring 53 appliesa rearward biasing force to the snap ring 75. Furthermore, a gap 76 isformed between the snap ring 75 and the rear cover 22.

In such a structure, the limiter disc spring 53 applies frontwardbiasing force to the bottom portion 21 a of the front cover 21. Further,the limiter disc spring 53 applies rearward biasing force to the snapring 75. In other words, the limiter disc spring 53 does not apply forceto the front cover 21 that moves it away from the rear cover 22. It isobvious that the limiter disc spring 53 also does not apply force to therear cover 22 that moves it away from the front cover 21. Thus, pressingforce for forcing the front cover 21 toward the rear cover 22 does notneed to be applied when joining the front cover 21 to the rear cover 22.Accordingly, the damper 14 can be easily assembled. In such a structure,the bottom portion 21 a of the front cover 21 and the snap ring 75 formthe separation restriction member. The bottom portion 21 a functions asa first restriction portion, and the snap ring 75 functions as a secondrestriction portion.

The collar portions 32 c and 33 c (i.e., plates 32 and 33) may beslightly deformed by the biasing force of the limiter disc spring 53. Insuch a case, the deformed collar portions 32 c and 33 c contact thecovers 21 and 22, respectively. In such a structure, the biasing forceof the limiter disc spring 53 applied to the covers 21 and 22 is muchsmaller than that of the prior art. Therefore, a pressing force actingto move the covers 21 and 22 away from each other is subtly applied tothe covers 21 and 22.

The covers 21 and 22 may be fixed together through fixing processesother than welding. For instance, the covers 21 and 22 may be fixed toeach other by rivets. In such a case, a seal ring (e.g., O-ring) forpreventing the leakage of lubricant oil from the outer case 23 ispreferably arranged at a region of contact between the covers 21 and 22.Such a structure obtains the same advantages as the first embodiment.

A second embodiment of the present invention will now be discussed withreference to FIGS. 7 to 12.

FIG. 7 is a cross-sectional view showing a damper 114 according to thepresent invention. In FIG. 7, reference number 101 denotes a damperdevice, reference number 102 denotes a limiter plate, reference number103 denotes a limiter disc spring serving as a first biasing member, andreference number 23 denotes an outer case serving as a housing. Thedamper 114 has the same basic structure as a damper used in a torqueconverter. The damper 114 includes a plurality of damper springs 42.Each damper spring 42 is arranged between a first plate 106 and a secondplate 107 and accommodated in a spring accommodation hole 40 formed bythe first plate 106 and the second plate 107. Each of the first plate106 and the second plate 107 has an inner circumference portion that islocated radially inward from the spring accommodation hole 40 and anouter circumferential portion that is located radially outward from thespring accommodation hole 40.

A circular central disc 108 is arranged between the first plate 106 andthe second plate 107. The damper spring 42 are elastically deformed whenthe central disc 108 rotates relative to the first plate 106 and thesecond plate 107. Although the detail is not shown in FIG. 7, the firstplate 106 and the second plate 107 are formed in such a manner that eachof the outer circumference portions is arranged at a distance from thecentral disk 108 in the axis S so as not to contact with the centraldisk 108, while the inner circumference portions are contactable in aslipping manner with the central disk 108. An intermediate member 109 isarranged radially inward from the central disc 108 and coupled to twodamper springs 42, which are paired and arranged in series. A firstfriction member 52 is arranged at the peripheral portion of the centraldisc 108 on each of the two surfaces that are opposed to each other inthe axial direction. The ring-shaped limiter plate 102 is arranged atthe peripheral portion of on one side of the central disc 108. Thelimiter disc spring 103 arranged between the outer case 23 and thelimiter plate 102 applies biasing force to the limiter plate 102. Theouter diameter of the central disc 108 may be reduced, and acircumferential plate formed from a material allowing easy arrangementof the first friction member 52 may be attached to the outercircumference of the central disc 108 in lieu of the central disc 108.

FIG. 8 is a front view (include partial cross-section) showing thedamper device 101 alone. A plurality of spring holders 122 projectradially inward from the ring-shaped central disc 108, and two dampersprings 42 are arranged in series between the adjacent spring holders122. A separator 123 is arranged between the damper springs 42 that arearranged in series. The separator 123 projects out from the outercircumference of the ring-shaped intermediate member 109, which issupported by a hub flange 30 of a hub 28. Accordingly, when the rotationof the central disc 108 relative to the first plate 106 and the secondplate 107 is fast, the damper springs 42 are compressed. However, insuch a case, the intermediate member 109 rotates and thereby uniformlycompresses the damper springs 42 that are arranged in series.

The hub 28, which includes a shaft hole 112, is arranged at the centerof the damper 114, and the hub 28 is fixed to an inner portion 124 ofthe first plate 106. The outer case 23 is formed by welding the frontcover 21, which serves as the first cover and functions as a fly wheel,to the rear cover 22, which serves as the second cover. A sleeve 22 c isformed at the center of the rear cover 22. The sleeve 22 c and the hub28 are concentric.

As shown in FIG. 9, which is a partially enlarged view of a centralshaft portion, the inner portion 124 of the first plate 106 is fixed tothe hub flange 30 of the hub 28 by rivets 31. The hub flange 30 includesa first disc portion 30 a, a second disc portion 30 b, and a third discportion 30 c, which lie along concentric circles and have differentouter diameters. The intermediate member 109 is rotatably supported bythe outer circumference of the third disc portion 30 c. A hysteresisdisc spring 57 serving as the second biasing member is fitted andattached to the smallest first disc portion 30 a. A hysteresis washer 61and a second friction member 56 are fitted and attached to the seconddisc portion 30 b.

The hysteresis washer 61 and the second friction member 56 are arrangedbetween the surface 133 of the third disc portion 30 c, which has thelargest outer diameter, and the hysteresis disc spring 57, which isreceived by the inner portion 124 of the first plate 106. Therefore, thebiasing force of the hysteresis disc spring 57 acts on the hysteresiswasher 61 and the second friction member 56, and frictional force forsuppressing rotation of the second friction member 56 relative to thehysteresis washer 61 is generated. An engagement piece 61 b, which isbent to be L-shaped, is formed at the outer circumference of thehysteresis washer 61. The engagement piece 61 b is fitted to anengagement hole 136 formed in the inner portion 124.

Engagement pieces 135 that are bent to be L-shaped are arranged at theouter circumference of the second friction member 56. The engagementpieces 135 engage with engagement grooves 137 formed in the intermediatemember 109. Therefore, although the intermediate member 109 is rotatedwhen the damper springs 42 are compressed, the engagement pieces 135restrict the rotation. The engagement grooves 137 formed in theintermediate member 109, which are longer than the engagement pieces135, are rotated by a predetermined angle without any restrictions fromthe engagement pieces 135 but come into contact with the engagementpieces 135 when rotated by a certain angle. In other words, theengagement pieces 135 engage the engagement grooves 137 with a margin ofa predetermined rotation angle.

When the compression of the damper spring 42 rotates the intermediatemember 109 by a predetermined angle and the distal end of the engagementgroove 137 comes into contact with the engagement piece 135 of thesecond friction member 56, the second friction member 56 rotates withthe intermediate member 109. However, the biasing force of thehysteresis disc spring 57 is applied to the second friction member 56.This produces a predetermined slip frictional force during the rotation.Accordingly, a large impact torque is alleviated and absorbed by theslip friction of the second friction member 56 when the damper springs42 are compressed. This allows for the employment of a spring having arelatively low spring constant as the damper spring 42.

A drive plate 117 is fastened by screws to the front cover 21 by way ofa coupling member 125, which is welded to the peripheral portion of thefront cover 21. The drive plate 117 is coupled to the crankshaft 12 a. Acenter portion 121 fitted to a center hole 126 of a crankshaft 12 a isformed in the center of the front cover 21. Therefore, the torque of thecrankshaft 12 a is transmitted to the outer case 23 through the driveplate 117 to rotate the damper device 101. Spline teeth are formed inthe outer circumference of the limiter plate 102. The spline teeth aremated with spline grooves formed in the inner circumferential surface ofthe outer case 23.

The limiter plate 102 is rotated with the outer case 23 and pushed bythe limiter disc spring 103. This rotates the central disc 108, which isarranged between the limiter plate 102 and the front cover 21. In otherwords, the first friction members 52 are formed on the two surfaces ofthe central disc 108. This rotates the limiter plate 102 without anyslipping. Then, the rotational torque of the central disc 108 istransmitted to the first plate 106 by the damper springs 42. Thisrotates the input shaft 16 serving as an output member fitted to theshaft hole 112 of the hub 28.

Normal impact torque is absorbed by the compressing deformation of thedamper spring 42. When the compressed amount of the damper springs 42becomes large, the second friction member 56 restricts rotation of theintermediate member 109 resulting from the compression of the dampersprings 42. In other words, the impact torque is partially absorbed bythe friction rotation of the second friction member 56. If a largerimpact torque is generated, the impact torque is alleviated by anauxiliary damper spring 138 arranged in the damper device 101.

FIG. 10 shows a state in which the damper of the second embodiment isattached to a power transmission mechanism. The crankshaft 12 a iscoupled to the drive plate 117. Therefore, the drive plate 117 and theouter case 23 are rotated by the crankshaft 12 a, and the rotationaltorque is transmitted from the central disc 108 to the first plate 106.This rotates and drives the input shaft 16 fitted to the shaft hole 112of the hub 28.

If a large torque acts on the central disc 108 of the damper device 101,the central disc 108 slips and idly rotates. In the present invention,the outer case 23 is filled with lubricant oil, and the critical torqueat which the central disc 108 spins is substantially constant. In otherwords, the lubricant oil prevents the engagement surface of the frictionmember from rusting. This keeps the friction coefficient constant.

In the damper 114, the outer case 23 is filled with the lubricant oil.Therefore, the central disc 108, the first plate 106, the second plate107, the intermediate member 109, the damper spring 42, the limiterplate 102, the second friction member 56, and the like of the damperdevice 101 arranged in the outer case 23 may be lubricated. Inparticular, the first friction member 52 at the peripheral portion ofthe central disc 108 does not rust.

FIGS. 11( a) to 11(c) are schematic diagrams of the damper device 101.FIG. 11( a) shows the damper device 101 shown in FIGS. 7 and 8.Reference numeral 42 denotes a damper spring, reference numeral 108denotes a central disc, reference numeral 109 denotes an intermediatemember, reference numeral 106 denotes a first plate, reference numeral56 denotes a second friction member, and reference numeral 137 denotesan engagement groove.

When the central disc 108, which serves as the torque input sideportion, moves relative to the first plate 106, which serves as thetorque output side portion, that is, when the central disc 108 movestoward the right and approaches the first plate 106 and the distancebetween the central disc 108 and first plate 106 decreases, the twodamper springs 42 that are in series are compressed. Further, a smallslip friction is generated between the central disc 108 and the firstplate 106. However, the slip friction is small and such that it does notinfluence the damper effect of the damper device 101.

In the damper of FIG. 7, the small slip friction is obtained by astructure in which the central disc 108 is arranged between the innersides of the first plate 106 and the second plate 107. The intermediatemember 109 moves toward the when the damper springs 42 are compressed.When the movement distance of the intermediate member 109 reaches apredetermined length, the second friction member 56 moves and generatesslip friction with the first plate 106, which serves as the torqueoutput side portion. The slip friction reaches a level of a certainextent, and the energy of the impact torque may be absorbed as thedamper springs 42 are compressed. The movement distance of theintermediate member 109 when the second friction member 56 starts toslide is determined by the length of the engagement groove 137 formed inthe intermediate member 109.

FIG. 11( b) shows a state in which the engagement groove 137 is formedin the central disc 108, and the second friction member 56 is fitted tothe engagement groove 137.

When the central disc 108, which serves as the torque input sideportion, moves toward the right and approaches the first plate 106 andthe distance decreases between the central disc 108 and the first plate,the two damper springs 42 that are arranged in series are compressed. Asmall slip friction is generates between the central disc 108 and thefirst plate 106. However, the slip friction is small and such that itdoes not influence the damper effect of the damper device 101.

The central disc 108 includes the engagement groove 137, and the secondfriction member 56 engages the engagement groove 137. The damper device101 is configured such that when the movement distance reaches apredetermined length, the second friction member 56 moves and generatesthe slip friction with the first plate 106, which becomes the torqueoutput side portion.

FIG. 11( c) shows a structure in which a single damper spring 42 isarranged between the spring holders 122 of the central disc 108. Theother parts are the same as the structure of FIG. 11( b). In otherwords, by attaching the second friction member 56, the damper of thesecond embodiment absorbs the energy of the impact torque through theslipping of the second friction member 56. Thus, the damper springs 42do not have to be arranged in series.

FIG. 12 is a cross-sectional view showing a third embodiment of a damperaccording to the present invention. In FIG. 12, reference numeral 139denotes a central disc, reference numeral 140 denotes a first plate,reference numeral 141 denotes a second plate, and reference numeral 142denotes an output side disc serving as a torque output side portion.

The central disc 139 is arranged between and fixed by the first plate140 and the second plate 141. The central disc 139, the first plate 140,and the second plate 141 form a torque input side portion. The outputside disc 142, which serves as the torque output side portion, isarranged on the inner circumferential side of the substantiallyring-shaped central disc 139. The output side disc 142 is arrangedbetween the first plate 140 and the second plate 141.

A damper spring 42 is accommodated in a spring accommodation hole 40formed by the first plate 140 and the second plate 141. The output sidedisk 142 has an inner circumference portion that is located radiallyinward from the spring accommodation hole 40 and an outer circumferenceportion that is located radially outward from the spring accommodationhole 40. Although the detail is not shown in FIG. 12, the first plate140 and the second plate 141 are formed in such a manner that the firstplate 140 and the second plate 141 are contactable in a slipping mannerwith the inner circumference portion of the output side disc 142. Thedamper spring 42 is elastically deformed when the first plate 140 andsecond plate 141 and the output side disc 142 are torsion rotatedrelative to each other. A first friction member 52 is arranged on eachof the two opposite surfaces at the peripheral portion of the centraldisc 139. A ring-shaped limiter plate 102 is arranged on one side of theperipheral portion of the central disc 139. Biasing force is applied tothe limiter plate 102 by a limiter disc spring 103 serving as a firstbiasing member arranged between the limiter plate 102 and the outer case23.

Accordingly, compression of the damper springs 42 alleviates impacttorque within a certain range. However, if a large torque that exceeds alimit is generated, the central disc 139 slips and relives the impacttorque. This aspect is the same as the damper of the second embodimentshown in FIG. 7. However, the damper shown in FIG. 12 has a structure inwhich the first plate 140 and the second plate 141 holding the centraldisc 139 in between form the torque input side portion, and the outputside disc 142 is discretely provided.

The inner portion of the output side disc 142 is curved and fixed to ahub flange 30 of a hub 28 by rivets 31. The hub flange 30 includes afirst disc portion 30 a, a second disc portion 30 b, and a third discportion 30 c, which are concentric to each other and have differentouter diameters. A hysteresis disc spring 57 serving as the secondbiasing member is fitted and attached to the smallest first disc portion30 a, and a hysteresis washer 61 and the second friction member 56 arefitted and attached to the second disc portion 30 b.

The hysteresis washer 61 and the second friction member 56 are arrangedbetween the third disc portion 30 c, which has the largest outerdiameter, and the hysteresis disc spring 57, which is received by theinner portion of the output side disc 142. Therefore, the biasing forceof the hysteresis disc spring 57 acts on the hysteresis washer 61 andthe second friction member 56. This generates frictional forcesuppressing the relative torsion rotation of the second friction member56 and the hysteresis washer 61. An engagement piece 61 b bent to beL-shaped is arranged on the outer circumference of the hysteresis washer61. The engagement piece 61 b is fitted to the engagement hole 136formed in the inner portion of the output side disc 142.

An engagement piece 135 bent to be L-shaped is also arranged on theouter circumference of the second friction member 56. The engagementpiece 135 is engaged with an engagement groove formed in the innercircumference of the second plate 141. Therefore, when the compressionof the damper spring 42 generates relative torsion rotation between theoutput side disc 142 and the second plate 141, the rotation isrestricted by the engagement piece 135 of the second friction member 56.The engagement groove in the second plate 141 is longer than theengagement piece 135, rotated by a predetermined torsion angle withoutany restrictions, and come into contact with the engagement piece 135when rotated by a certain constant angle. In other words, the engagementpiece 135 engages the engagement groove with a margin of a predeterminedrotation angle.

When the compression of the damper spring 42 rotates the output sidedisc 142 by a predetermined angle, the distal end of the engagementgroove comes into contact with the engagement piece 135 of the secondfriction member 56, and the second friction member 56 rotates with thesecond plate 141. However, the biasing force of the hysteresis discspring 57 is applied to the second friction member 56. This generates apredetermined slip frictional force during rotation. Therefore, a largeimpact torque is alleviated and absorbed by the slip friction of thesecond friction member 56 when the damper spring 42 is compressed.

1. A damper arranged in a torque transmission path that transmits torquefrom a power source to an output member rotated about a predeterminedaxis, the damper comprising: a housing rotated about the axis andincluding a first cover and a second cover arranged along the axis, inwhich the first and second covers are joined to form a liquidaccommodation chamber which accommodates a liquid; a damper devicearranged in the liquid accommodation chamber and capable of absorbingtorque fluctuation transmitted through the housing; a limiter mechanismarranged in the liquid accommodation chamber and including an input sideportion located at an input side of the torque transmission path, anoutput side portion arranged opposing the input side portion and locatedat an output side of the torque transmission path, and a limiter biasingmember which applies a biasing force to at least one of the input sideportion and the output side portion in a direction that the input sideportion and the output side portion approach each other; and aseparation restriction member arranged in the liquid accommodationchamber, in which the separation restriction member restricts relativemovement of the first cover and the second cover caused by the biasingforce from the limiter biasing member in a direction that separates thefirst cover and second cover from each other.
 2. The damper according toclaim 1, wherein: the separation restriction member includes a firstrestriction portion arranged on one side of the limiter mechanism in theaxial direction and a second restriction portion arranged on the otherside of the limiter mechanism in the axial direction; and the first andsecond restriction portions are arranged so as to maintain the distancetherebetween.
 3. The damper according to claim 2, wherein the separationrestriction member is supported by a downstream side member, which islocated downstream from the limiter mechanism in the torque transmissionpath, so as to be integrally rotatable with the downstream side memberin a state in which movement of each of the first and second restrictionportions in the axial direction is suppressed.
 4. The damper accordingto claim 1, wherein the limiter mechanism is arranged inward from thedamper device in a radial direction of the damper that is orthogonal tothe axis.
 5. The damper according to claim 4, further comprising: acoupling member coupled to the output member in the housing in a mannerintegrally rotatable with the output member, wherein the coupling membersupports the separation restriction member in an integrally rotatablestate.
 6. The damper according to claim 1, further comprising: ahysteresis mechanism arranged in the liquid accommodation chamber, inwhich the hysteresis mechanism is configured to function when a rotationdifference of the housing and the output member in a rotation directionabout the axis becomes equal to a predetermined rotation difference,wherein the hysteresis mechanism is arranged inward from the damperdevice and the limiter mechanism in a radial direction of the damperthat is orthogonal to the axis.
 7. The damper according to claim 6,further comprising: a cylindrical coupling member coupled to the outputmember in the housing in a manner integrally rotatable with the outputmember; and an annular supporting member arranged on a circumferentialside of the coupling member and supported by the coupling member in astate integrally rotatable with the coupling member; wherein thecoupling member includes a flange arranged at a position separated fromthe supporting member in the axial direction along the axis and arrangedto form an installation space between the flange and the supportingmember in the axial direction; the hysteresis mechanism includes afriction generation unit, which is arranged in the installation space,and a rotation unit, which is rotated with the housing by torquetransmitted from the housing when a rotation difference between thehousing and the output member becomes equal to a predetermined rotationdifference; and the friction generation unit is configured to generatefrictional force with the rotation unit that suppresses rotation of therotation unit when the rotation unit rotates with the housing.
 8. Thedamper according to claim 7, wherein: the rotation unit includes acontacted portion arranged in the installation space; and the frictiongeneration unit includes a contact member, which is movable in the axialdirection and contacts the contacted portion of the rotation unit, and ahysteresis biasing member, which applies a biasing force to the contactmember so that the contact member presses the contacted portion.
 9. Thedamper according to claim 4, wherein the damper device includes: a firsttorque transmission unit arranged in the housing in a torquetransmittable state; a second torque transmission unit arranged at thesame position as the first torque transmission unit in the radialdirection of the damper and configured to be torque transmittable to theoutput member; and an elastic member which is elastic in acircumferential direction of which center is the axis and arranged in atorque transmittable state between the first torque transmission unitand the second torque transmission unit in the circumferentialdirection.
 10. The damper according to claim 9, wherein the first torquetransmission unit is arranged in the housing in a state integrallyrotatable with the housing, and the input side portion of the limitermechanism is connected to the second torque transmission unit in atorque transmittable state.
 11. The damper according to claim 1, whereinthe covers are joined by welding a first fixing portion of the firstcover to a second fixing portion of the second cover, which faces towardthe first fixing portion.
 12. A damper incorporated in a powertransmission mechanism for a hybrid vehicle, the damper comprising: ahousing including a first cover and a second cover joined with eachother, in which the housing is coupled to a drive plate and filled withlubricant oil; and a damper device arranged in the housing, the damperdevice including: a plurality of damper springs; a central disc, whichis a torque input side portion; a first friction member arranged in aperipheral portion of the central disc; a limiter plate arranged to facetoward the first friction member; a first biasing member which pushesthe limiter plate so that the central disc is arranged between thelimiter plate and the housing; a hub having a shaft hole arranged at acenter of the damper device and fitted to an output member; a firstplate and a second plate, which are torque output side portions,arranged on opposite sides of the central disc; a second friction memberarranged between the torque output side portion and the central disc;and a second biasing member which biases the second friction member,wherein the second friction member suppresses relative rotation of thecentral disc and the torque output side portion that is greater than orequal to a certain level with slip friction generated when the dampersprings are deformed.
 13. The damper according to claim 12, whereinouter circumference portions of the first plate and the second plate arespaced from the central disc so as not to contact the central disc, andinner circumference portions of the first plate and second plate arecontactable in a slipping manner with the central disc.
 14. The damperaccording to claim 12, wherein the second friction member engages anengagement groove foamed in the central disc so as to be rotatablerelative to the central disc in a predetermined rotation angle range,and the second friction member generates a slip friction when a relativerotation angle between the central disc and the torque output sideportion becomes greater than or equal to a certain angle.
 15. The damperaccording to claim 12, wherein: the central disc is generallyring-shaped and includes an inner portion in which spring holders arearranged, in which two damper springs are arranged in series betweenadjacent ones of the spring holders; the hub includes a flangesupporting an intermediate member having an engagement groove; aseparator projecting from an outer circumference of the intermediatemember is arranged between the two damper springs; the second frictionmember engages the engagement groove of the intermediate member so as tobe rotatable relative to the intermediate member in a predeterminedrotation angle range; and the second friction member generates slipfriction when a relative rotation angle between the central disc and thetorque output side portion becomes greater than or equal to a certainangle.
 16. The damper according to claim 12, wherein: the hub includes aflange having first to third disc portions that are concentric and havedifferent outer diameters, in which the second biasing member isattached to the first disc portion having the smallest diameter, awasher and the second friction member are attached to the second discportion having an intermediate outer diameter, and the washer and thesecond friction member are arranged between the first plate and thethird disc portion having the largest diameter in a state in which abiasing force of the second biasing member is applied; and an engagementpiece arranged in the washer engages with an engagement hole of thefirst plate.
 17. A damper incorporated in a power transmission mechanismfor a hybrid vehicle, the damper comprising: a housing including a firstcover and a second cover joined with each other, in which the housing iscoupled to a drive plate and filled with lubricant oil; and a damperdevice arranged in the housing, the damper device including: a centraldisc; a first friction member arranged at a peripheral portion of thecentral disc; a limiter plate arranged to face toward the first frictionmember; a first biasing member which pushes the limiter plate so thatthe central disc is arranged between the limiter plate and the housing;a hub having a shaft hole arranged at a center of the damper device andfitted to an output member; a first plate and a second plate arranged atopposite sides of the central disc and coupled to the central disc, inwhich the first plate and second plate configure a torque input sideportion with the central disc; an output side disc, which is a torqueoutput side portion, fixed to the hub and arranged between the firstplate and the second plate; a plurality of damper springs accommodatedin a spring accommodation hole formed between the first plate and thesecond plate, in which the damper springs elastically couple the torqueinput side portion and the output side disc; a second friction memberarranged between the output side disc and the torque input side portion;and a second biasing member which biases the second friction member,wherein the second friction member suppresses relative rotation of thetorque input side portion and the output side disc that is greater thanor equal to a certain level with slip friction generated when the dampersprings deform.
 18. The damper according to claim 17, wherein the firstplate and the second plate are contactable in a slipping manner with aninner circumference portion of the output side disc.
 19. The damperaccording to claim 17, wherein the second friction member engages anengagement groove formed in at least one of the first plate and thesecond plate so as to be rotatable in a predetermined rotation anglerange relative to at least one of the first plate and the second plate,and the second friction member generates a slip friction when a relativerotation angle between the torque input side portion and the output sidedisc becomes greater than or equal to a certain angle.
 20. The damperaccording to claim 17, wherein: the output side disc is generallyring-shaped and includes a peripheral portion in which spring holdersare arranged, in which two damper springs are arranged in series betweenadjacent ones of the spring holders; the ring-shaped central discincludes an inner portion supporting an intermediate member having anengagement groove; a separator projecting from an inner circumference ofthe intermediate member is arranged between the two damper springs; thesecond friction member engages the engagement groove of the intermediatemember so as to be rotatable relative to the intermediate member in apredetermined rotation angle range; and the second friction membergenerates slip friction when a relative rotation angle between thetorque input side portion and the output side disc becomes greater thanor equal to a certain angle.
 21. The damper according to claim 17,wherein: the hub includes a flange having first to third disc portionsthat are concentric and have different outer diameters, in which thesecond biasing member is attached to the first disc portion having thesmallest diameter, a washer and the second friction member are attachedto the second disc portion having an intermediate outer diameter, andthe washer and the second friction member are arranged between theoutput side disc and the third disc portion in a state in which abiasing force of the second biasing member is applied; and an engagementpiece arranged in the washer engages with an engagement hole of theoutput side disc.